Electrochemical sensors, especially electrochemical gas sensors, usually do not have an unlimited service life. A point in time at which the technical properties are no longer sufficient for accomplishing the measuring task is reached at a certain time. In electrochemical gas sensors, one of these properties may be, for example, the level of the output signal at a certain gas concentration. Such sensors should therefore be exchanged and replaced with new ones at certain intervals.
Both a safety engineering aspect and an economic aspect play a role concerning the point in time at which the replacement is necessary. From a purely safety engineering viewpoint, the sensor would be replaced at the shortest possible intervals (for example, yearly or more frequently) in order to rule out a failure with the highest possible probability. The drawback of doing so is that needlessly high costs are incurred.
From a purely economical viewpoint, a sensor would be replaced only when it was recognized as being defective. This defect may be determined during the calibration or also during a sensor self-test. The drawback here is that the measuring function is not guaranteed continuously, because replacement of the sensor cannot always be carried out in a short time.
A process for recognizing sources of error in amperometric measuring cells is known from DE 44 45 947 C2. The voltage of the potentiostat is slightly detuned here in order to calculate from this parameters that provide information on the state of use of the electrochemical sensor. It is displayed whether a sensor has been used up or damaged. However, the prior-art process provides no information on how long the sensor can still be used for measurement purposes.